Resistor grid



March 29, 1932. F. T. COPE ET AL RESISTOR GRID Filed Feb. 6, 1930 2Sheets-Sheet All Ime/mfom Patented Mar. 29, 1.932-

UNITED STATES PATENT orricE anatra a. corn AND ARTHUR H. VUGHAN, 0FSALEM, OHIO,ASSIGNORS T0 THE ELEC- TRIO FURNACE COMPANY, F SALEM, OHIO,A CORPORATION OF OHIO BESISTOR GRID Application tiled February e, 1930,Serial No.. 428,809.y

relates to metallic resistor cast, rolled or forged constructlon,

rllhe invention grids of for use in electric furnaces or kilns, and

more particularly to the cross sectional shape a of such grids and themeans for supporting the saine in the furnace or kiln.

lt is well known that metallic resistor grids of dierent pross sectionalshapes have been made and used in electric furnaces and l@ the like withvarious degrees of satisfaction and success.

ln the severe service'to which such resistor grids are subjected inlarge industrial furnaces, we have found that the following H propertiesare important in metallic resistor grids:

First, an eiiicient cross sectional shape for structural strength, so asto prevent sagging and warping under. stresses due to tempera- 2G turedierences, and to the weight of the rid; v

g Second, proper disposition of the heat radiating surface of the gridso as to liberate heat and radiate it to the work with the leastpossible interference from adjacent parts of the grid itself and fromsupporting means;

\ Third, ability of the grid to shed scale which may fall thereon fromthe material when the grid is placed beneath the material Folirth, suchcross sectional shape as will permit of soundness and homogeneity beingattained when the grid is made by casting;

Fifth, resistance to oxidation such as to enable grid to withstand thetemperatures at which it is operated.

To secure the necessary resistance to oxidation it is customary toemploy alloys containing nickel and chromium with varying amounts ofiron.

e have found that where the resistor is in the form of rolled'wire orribbon it is very diiiicult to attain the structural strength necessaryfor horizontal or inclined mountl" mg, which is very often desired. Withsuch resistors it is customary to employ supporting framework andadditional insulators and spacers to prevent displacement which mightoccasion short circuits.

These additional supporting means are not only expensive but theyinterfere considerably with free radiation of heat from all parts of theresistor and frequently prevent placing of the resistors in the mostadvantageous position.

lin order to radiate heat from the surface of the grid, ence betweenadjacent parts of the grid, we have used grids of the greater part ofaway from the furnace wall.

At times we have used a T-section with a tapered stem rib or flange,mounted so that t e stem extends toward the interior of the furnace; andalso a channel section havin tapered ribs or flanges extending towardthe interior of the furnace.

en we mount resistor grids near the licor or beneath the roof of afurnace, we support them at the end portions so that each of thestraight portions of the grid is loaded, as a beam, by its own weight.Such a method of mounting the grids has the advantage that there isnothing to prevent the free radiation gf heat from the entire length ofthe grid ars.

When it is desired to make the grids of cast alloys, it is extremelyimportant that their that the castings will be reasonably homogeneous,sound and free from internal cavities. This can only be attained whenthecross section is substantially uniform in thickness at all points,the maximum thickness being necessarily thin enough so that no partsolidifies appreciably later than other parts.

The object of the present invention is to 'provide a cross sectionalshape of resistor which we have found gives the best combination of theseveraldesirable features above referred to. This cross sectional shapeis in the form of a true Y, and is intended to be placed with the tailrib of the Y extending toward the interior of the furnace and away fromthe adjacent wall, preferably at a right angle thereto.

We have found that while other cross sectional shapes may excel the Y incertain respects, they are not suitable in others. For instance, aninverted V-shape, with tapered Gti auv

stantially a true Y- ribs, when placed in the floor of a furnace,possesses ideal scale shedding properties, but has been found to bestructurally very weak,

. as compared to the Y-section of substantially Y the same crosssectional area and the same over-all dimensions.

Such a section, when made by casting, is

j also likely to be unsound because of slow coolsurface for radiation,is almost the weakest structurally of all sections which have beentried.

The above and other'objects may be attained by constructing and mountingthe improved resistor grid in the manner illustrat- .ed in theaccompanying drawings, in which Figure 1 1s a transverse sectional viewthrough a furnace ofconventional type provided with the improvedresistor grids, taken substantially on the line 1-1, Fig. 2;

Fig. 2, a longitudinal sectional view through one end portion of thefurnace, takenon the line v2--2, Fig. 1; and

'Fig 3, an enlarged cross sectional view through the improved resistorgrid.

Similar numerals refer to similar parts throughout the drawings.

The invention consists primarily in the provision of a metallic resistorformed of a plurality of spaced parallel bars 10, ofsuitable heatresisting alloy suc-h as nickel-chromium containing varying amounts ofiron, which may be connected together at alternate ends, as b-y thereturn loopsor bends 11 to provide a continuous resistor.

The entire resistor may be cast in a single piece, each straight barthereof being of subhaped cross section, as best shown in Fig. 3, andincluding the angular fork or V-portion adapted to face toward theadjacent furnace wall and comprising the ribs 12 extending toward thewall at equal angles thereto, and the tail rib 13 preferably of greaterlength than theribs 12 and extending away from the adjacent furnace Wallat a right angle thereto.

The ribs 12 forming the V-portion may be of substantially the samethickness throughout their length and preferably have the an gular rearedges 14 arrangedto be located parallelto the adjacent furnace wallwhile the tail rib 13 is preferably tapered from the junction of theV-portion to its e'dge which may be rounded as at 15. I

rl`he sides of the ribs 12" of the angular fork or V-portion as well asthe sides of the' tail. portion 13 are preferably flat -as` shown inFig. 3 of the drawings.

It will be seen that the effect of shaping the resistor substantially asa true Y in cross section is to reduce the thickness and consequentlythe mass of metal at the junction of the V-portion and tail rib with theresult that there is very little difference in the thickness of themetal at the junction of the ribs as compared with the thickness of theseveral ribs themselves.

As above ointed out, a substantial uniformity in tie thickness of thesections is very important in the casting of the metals usually employedfor resistor grids because of the considerable shrinkage of such metalswhen cooling from tendency to produce shrinkage cavities in any portionof the casting which cools at a much slower'rate than the otherportions.

In applying the improved resistors to a furnace, such as illustratedconventionally in Figs 1 and 2, the resistors may he located adjacent tothe top, bottom and side walls 16, 17 and 18 respectively, asillustrated in these figures.

The upper grids may be located adjacent to the top wall 16 and supportedas by means of the ledges' 19, forme near the upper ends of the sidewalls, and by the refractory blocks 20 supported in any suitable manner,as by the bolts 21.

The'side grids may be supported adjacent to the side walls 18 as by thehooks or hangers 22 which engage the upper loops or bends of the grids,guides 23 being carried in the side walls for guiding the lower ends ofthe grids and permitting expansion and contraction thereof underchanging temperatures.

The hearth 24 may be supported upon spaced piers 25 having ledges 26 attheir bases for supporting the lower resistors spaced from the bottomwall or floor. It will be seen that the upper and lower resistors areboth supported as a beam.

From the above descri tion and the illustration in the accompanyingdrawings it will be seen that-a resistor grid is provided havin a true Ycross sectional shape, the tail rib of the Y facing toward the workwhile the open side or fork thereof is faced toward the adjacent greaterportion of the cross section of the resistor toward the interior of thefurnace and directing the major portion of the' heat radiated therefromtoward the work or interior of the furnace at an angle to the adjacentfurnace wall.

Where the Y-shaped grids are mounted beneath the work or beneath thehearth, the Ys are inverted with the tail ribs extending upward so thatscale falling from the work or hearth and striking of the grids willslide therefrom,preventing short-circuiting of the grids by scale pilingupon the same.

From the a ove it will be seen that a resistor grid is produced whichhas the best the molten state and the furnace Wall, thus disposing the'combination of lateral and beam strength, efficient disposition ofsurface for heat radiation, and ability to shed scale and dirt, andwhich can be cast satisfactorily if it is de- 5 sired to make the gridin this manner.

v We claim:

1. A resistor grid including a straight bar of substantially Y crosssectional shape and having an angular fork portion and a straight tailrib each having flat sides.

2. `A resistor grid including a straight bar of substantially Y crosssectional shape and having an angular fork portion and a tail rib, eachhaving Hat sides, the tail rib being tapered toward its edge.

3. A resistor grid including a straight bar of substantially Y crosssectional shape and having an angular fork portion and a tail rib, eachhaving fiat sides, the ribs of the fork portion being of uniformthickness throughout aid the tail rib being tapered toward its e ge.

4. A resistor grid including a straight bar of substantially Y crosssectional shape and having an angular fork portion and a tail rib eachhaving fiat sides. the tail rib being provided with a rounded edge.

5. A resistor grid including a straight bar of substantially Y crosssectional shape and having an angular fork portion and a tail rib, eachhaving flat sides, the ribs of the fork portion being of uniformthickness throughout and the tail rib being tapered toward its edge andhaving its edge rounded.

6. A resistor grid including a straight bar of substantially Y crosssectional shape, and having an angular fork portion and a tail rib eachhaving Hat sides, the ribs of the fork portion being of uniformthickness throughout.

In testimony that we claim the above, we

have hereunto subscribed our names.

FRANK T. COPE. ARTHUR H. VAUGHAN.

